// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// File provides direct encoding of bits with arithmetic encoder interface.
#ifndef DRACO_CORE_BIT_CODERS_DIRECT_BIT_DECODER_H_
#define DRACO_CORE_BIT_CODERS_DIRECT_BIT_DECODER_H_

#include <vector>

#include "draco/core/decoder_buffer.h"

namespace draco {

class DirectBitDecoder {
  public:
    DirectBitDecoder();
    ~DirectBitDecoder();

    // Sets |source_buffer| as the buffer to decode bits from.
    bool StartDecoding(DecoderBuffer *source_buffer);

    // Decode one bit. Returns true if the bit is a 1, otherwise false.
    bool DecodeNextBit() {
        const uint32_t selector = 1 << (31 - num_used_bits_);
        const bool bit = *pos_ & selector;
        ++num_used_bits_;
        if (num_used_bits_ == 32) {
            ++pos_;
            num_used_bits_ = 0;
        }
        return bit;
    }

    // Decode the next |nbits| and return the sequence in |value|. |nbits| must be
    // > 0 and <= 32.
    void DecodeLeastSignificantBits32(int nbits, uint32_t *value) {
        DRACO_DCHECK_EQ(true, nbits <= 32);
        DRACO_DCHECK_EQ(true, nbits > 0);
        const int remaining = 32 - num_used_bits_;
        if (nbits <= remaining) {
            *value = (*pos_ << num_used_bits_) >> (32 - nbits);
            num_used_bits_ += nbits;
            if (num_used_bits_ == 32) {
                ++pos_;
                num_used_bits_ = 0;
            }
        } else {
            const uint32_t value_l = ((*pos_) << num_used_bits_);
            num_used_bits_ = nbits - remaining;
            ++pos_;
            const uint32_t value_r = (*pos_) >> (32 - num_used_bits_);
            *value = (value_l >> (32 - num_used_bits_ - remaining)) | value_r;
        }
    }

    void EndDecoding() {}

  private:
    void Clear();

    std::vector<uint32_t> bits_;
    std::vector<uint32_t>::const_iterator pos_;
    uint32_t num_used_bits_;
};

}  // namespace draco

#endif  // DRACO_CORE_BIT_CODERS_DIRECT_BIT_DECODER_H_
